SANTA CLARA — Health officials confirmed this week at least three Bay Area residents in Santa Clara, San Francisco and Santa Cruz counties have contracted measles, two of them from the other person in the same airplane flight.

In February, a Santa Cruz County resident with measles was on an international flight that landed at San Francisco International Airport, according to the Santa Clara County Public Health Department. It’s unclear whether that person knew he or she had measles at the time.

Since then, two other passengers on that flight caught the disease — one from San Francisco and the other from Santa Clara County.

In a health advisory issued Tuesday, San Francisco health officials confirmed that a San Francisco adult had been diagnosed with measles — the first in the city since 2013.

“The general public is at very low risk of measles as a result of these cases. No other passengers contracted measles as a result of exposure on that flight,” Santa Clara County Public Health Department spokeswoman Britt Ehrhardt said in a statement issued to this news organization. “The flight was more than three weeks ago. Measles develops within 21 days of exposure. Public health investigators have not identified any evidence indicating that measles is spreading within the impacted counties.”

Ehrhardt said the department immediately responds to suspected measles cases. She could not confirm whether the three affected individuals had been vaccinated against the disease.

“In this case, we conducted a contact investigation to identify individuals who might have had contact with the Santa Clara County resident with measles while that person was contagious,” she said. “A contact investigation traces each place where the contagious individual might have spent time, then tries to identify each person who might have been exposed in those places. The Santa Clara County resident with measles did not go out in public while contagious with measles, so public notification was not indicated.”

The department did not issue a public health advisory in Santa Clara for this case.

“When public health actions are required to protect the health of the community, Public Health Department staff outline them immediately and would notify the medical community, partners, other appropriate parties, and the general public,” Ehrhardt said.

It appears to be the first diagnosed outbreak in the Bay Area this year. The diagnosis comes just days after the Centers for Disease Control and Prevention published a report saying that a measles outbreak in the Bay Area last year spread among families who did not vaccinate their children.

Measles is a highly contagious disease that spreads when someone who’s infected coughs and sneezes. Symptoms usually develop 10 to 12 days after exposure and can last seven to 10 days. Initial symptoms typically include a high fever, cough, runny nose, inflamed eyes and a rash that begins on the forehead and spreads throughout the body.

“Although measles is no longer endemic in the United States, measles epidemics overseas have resulted in imported cases and resulting secondary cases,” the San Francisco health advisory said, adding that there currently are measles epidemics in the Philippines, Indonesia, Israel, Ukraine, Romania, Brazil, and much of Western Europe.

The statement from Santa Clara County officials advises that “making sure you have all your immunizations is especially important for travelers, because measles is circulating in many countries outside the United States. Early immunization with MMR vaccine is recommended for infants ages 6-11 months before going on an international trip.”

Last year’s outbreak in the Bay Area, as detailed by the CDC report released Friday, started with a Santa Clara County family who had traveled to England in February 2018 and whose 15 year-old son, who was not vaccinated, contracted the disease. While he was later quarantined at home, he had attended events in the days after returning where several people he came into contact with eventually contracted the illness.

The diagnosed cases included two young brothers whose mother initially lied to public health investigators about their immunization status and later acknowledged they were not vaccinated after they showed symptoms of measles and after their uncle, an Alameda County resident, was diagnosed with measles. In an attempt to contain the outbreak, public health investigators contacted hundreds of people the patients could have come into contact with across 10 counties in California and Nevada.

Only one of the seven people across Santa Clara and Alameda counties who contracted measles during that outbreak was vaccinated, according to the report. Ehrhardt said there was one other case, in April 2018, of a Santa Clara County resident who contracted measles, also through international travel. That case wasn’t related to the outbreak detailed by the CDC.

Contra Costa County’s last reported case of measles was in August, its first since 2015 when California saw a large outbreak of the disease. San Mateo County also saw one diagnosed case of measles last year — its first since it had four cases in 2015. A spokesman for San Mateo County’s health department said it could not comment on current measles investigations.

Annie Sciacca is a reporter at Bay Area News Group, where she writes about business and economy topics that affect consumers throughout the region. She joined the company in 2016 after three years at the San Francisco Business Times, where she covered the food, retail, manufacturing and hotels industries throughout the Bay Area. She holds an undergraduate degree from UC Berkeley and a master's degree in political science from San Francisco State University.